The present invention relates to a CATV system. More specifically, the invention to a polling signal generator in a CATV system for periodically transmitting a polling signal to terminal units to initiate the transmission of specific data from the terminal units.
A CATV system serves to transmit a variety of programs to television sets of terminal units installed in subscriber's homes through coaxial cables. Many CATV systems are capable of performing bidirectional simultaneous communications in addition to program transmission wherein the center simultaneously transmit information to a number of the terminal units and receives information back from them. Specifically, predetermined functions in the terminal units have to be periodically or irregularly polled. This polling operation is conducted by transmitting a down data signal to the terminal units, receiving up signals in reply to the down data signal and comparing the command in the down data signal therewith. However, in order to generate such a down data signal for polling the terminal units, a large-sized computer has heretofore been necessary. Such a computer cannot easily be transported around the system, as would be desirable.
It is thus an object of the present invention to provide a polling pattern generator for a CATV system which eliminates the aforementioned drawbacks, is portable, has a simple construction, and can periodically generate a polling pattern for polling the terminal units.